1. Field of Invention
The present invention relates generally to a semiconductor substrate processing apparatus. More specifically, the invention relates to an apparatus and method for providing pressure control within a semiconductor processing chamber.
2. Background of the Invention
In plasma processing of semiconductor substrates, certain processing steps require the regulation of chamber pressures and removal of gases and process residues from a processing chamber. Typically, pressure regulation and the removal of such gases and process residues are facilitated through the use of a vacuum pump and throttle valve coupled to an exhaust port of the processing chamber.
FIG. 1 depicts an exemplary semiconductor substrate processing system 10 having a throttle valve 38 and vacuum pump 40. An example of such a chamber is described by Collins in U.S. Pat. No. 5,707,486, issued Jan. 13, 1998.
The processing system 10 comprises a process chamber 44 having a bottom 26, sidewalls 24, and a lid 22 that define a chamber volume 12. A substrate support pedestal 18 is disposed in the process chamber 44 and supports a workpiece or substrate 20 (i.e., a wafer). Generally, a gas supply 42 is coupled to the process chamber 44 via one or more ports positioned either in the lid 22 or sidewalls 24. The gas supply 42 provides process and other gases to a processing region 14 above the substrate 20.
The chamber volume 12 is evacuated via the vacuum pump 40 coupled to the process chamber 44 typically through an exhaust port 36 positioned below the level of the substrate 20. The throttle valve 38 is coupled disposed between the process chamber 44 and the vacuum pump 40. A pressure control volume 46 is defined as the internal volume of the process chamber 44 upstream of the throttle valve 38. Generally, on typical systems, the chamber volume 12 and the pressure control volume 46 are substantially identical. Pressure is regulated within the process chamber 44 by actuating the throttle valve 38. Changes to the chamber pressure effectuated by the throttle valve 38 are propagated through the entire pressure control volume 46.
Although pressure control using the system described above has proven to be robust, the large size of the pressure control volume delays changes in chamber pressure in response to pressure control measures (i.e., such as throttle valve actuation). Additionally, since the pressure control volume is substantially equal to the chamber volume, the resonance time of gases within the chamber is long. Long resonance times of etchants result in other components within the chamber having to be replaced frequently (i.e., high cost of consumables) while long resonance times of reaction by-products may contribute to chamber and wafer contamination. Moreover, large volumes generally require more gases to obtain desired process concentrations, longer purge times, and greater processing cost.
Therefore, there is a need for an apparatus that facilitates pressure control in a semiconductor processing chamber while reducing the volume of the pressure control region.